Cavity resonator magnetron



Feb. 4, 1947. E. G. LINDER 2,415,253

CAVI TY RESONATOR MAGNETRON Original Filed 001;. 24, 1940 I'mnentor W 1 ERNEST E.LINDER 043' BB g I Patented Feb. 4, 1947 CAVITY RESONATOR MAGNETRON -Ernest G. Linder, Princeton, N. J., assignor to America,,a corporation of Radio Corporation of i I Delaware original'application October 24., 1940, Serial No. i 362,487. Divided and this-application October 30, 1943;.Serial No. 508,348"-" This application isa United States application, upon whichPatent No. 2,348,986 was granted May 16, 1944, Serial No, 362,487,; filed October 24, 1940, entitled Resonant cavity magnetron, and assigned to the same as-' signee as the instant application.

This invention relates to magnetrons and particularly to resonant cavity magnetrons in which the cavity acts as a tank circuit.

Magnetrons, usingapluralityof arcuate shape anodes, are well known. The arcuate shape anodes are usually. connected to tank circuits or in some devices the anodes themselves form the tank circuit as shown in Ernest G. Linderis U. S. Patent No. 2,233,482 granted on March 4, .1941, for Anode tank circuit oscillators. In suchdevices electrons, under the influence of a magnetic field,

travel along curved paths toward the anode. Some of the electrons give up their energy to initiate or reinforce oscillatory currents in the tank circuit. i

In the present invention the anode electrode of a magnetron. includes a slit or a plurality of slits. A. resonant cavity member also including a slit, is attached to the anode so that a slit in the anode substantially coincides with the slit in the resonant cavity member. Asthe electrons spiral past the slits, some of the electrons deliver energ to reinforoe'or establish within the cavity'standing electromagnetic waves.

It is an object of the invention to provide an improved means for detecting,amplifying or generating ultra high frequency electromagnetic waves. Another object is to provide means whereby a magnetron is provided With a resonant cavity tank circuit. Another object is to provide means whereby a plurality of resonant cavity members are effectively connected to the anode electrode of a magnetron An additional object is to provide means for adjusting the phase relations of: standing waves established in a plurality of resonant cavities .which are connected'to a magnetron. The, invention will be described by referring to the accompanying drawing in which Fig; 1 is a.

perspective view of oneembodiment of the invention; Figures 2a. and .21) are plan and elevationalviews, respectively; of the anode and resonantcavity members .employedinsaid one em-:

3 was? (c1.. s s-c division of my copending ing means. Similar reference characters areapr plied to similar elements throughout the drawing.

Referring to Fig-. 1 within an evacuated envelope l are mounted a substantially cylindrical anode 3 and a pair of substantially cylindrical members 5, l which each include a resonant eav:

ity. The anode includeslongitudinalslits 9, H the members '5, l' include, respectively, longitudi nal slits l3, l5. The members 5,"! are secured by soldering or the. like to. the anode-so-that their respective slits coincide. It should be, understood that the anode and cavity members may be fabricated in any desired manner, and the space within the anode. may be considered as part of theresonant cavity. Acathode ll extends along the axis of the anode. A magnetic field is estab-;

lished by a permanent magnet l9, electromagnet, or solenoid. cylindrical or conical polepieces may be attached to increase the flux which surrounds and is sub stantially parallel to the. cathode.

The circuit connections are as follows: The

cathode is connected to a battery 2| and rheostat 23. The anode is connected to the positive terminal of a battery 25 whose negative terminal is connected to the cathode circuit. A pickup loop 21 is inserted through a suitable aperture 29 in one of the resonant cavities. The pickup 1001 may bev terminated in a load circuit, such as a dipole antenna.

Underpthe influence of the magnetic field elecwardly toward the anode.

lished within the cavities.

netic standing waves within the cavities. The distribution of the fields is shownin Fig. 3 in which the abscissa represents the transverse axis through the cavities, and anode, and theordinate represents the'electric intensity E. Since. the

cathode is perpendicular to the electric field, it

offers substantially no interference to the waves. The device may be used as adetector by means of the circuit shown in Fig. 4. The pickup loop 3! is connected through a transmission line .33 to;

The anode is connected a dipole antenna 35. through a transformer primary 3! and battery 39 to the cathode circuit 4!. The secondary of the transformer is connected to a signal indicator, such as telephon receivers 43.

The slitted anode arrangement may be used If a permanent magnet is used,v

' edto a resonance indicator.

with a plurality of resonant cavity members as shown in Fig. 5. The anode electrode 45 includes four slits 41. While the resonant cavities may be of any suitable shape, such as a rectangle cavity, cuneiform members 49 may be used. The apex of each member is slitted so that the members maybe jointed to the anode so that each of the slits of the anode coincide with a slit in the apex of an attached resonant cavity member. The resonant cavity members may be coupled by an adjustable length of concentric line 5| to regulate the phases of the standing waves. The load circuit may be connected to a concentric line 53 which includes a coupling loop 55 terminating Within one of the cavities. The operation of the multicavity device is essentially the same as that of a single or dual resonant cavity magnetron.

As a first approximation the resonant wave length of a rectangular cavity may be determined by the formula where xo=2b and b equals the cavity width xe=wave length in free space L=the cavity length The foregoing formula applies to a rectangular cavity in which the height has a negligible effect on Wave length. The formula applies approximately to a wedge shape cavity in which the Wedge angle is small. Furthermore the anode electrode is connected to the wedge shape cavity and effects its resonant wave length. In practice waves of varying length are applied to the cavity and their effect determined by a probe inserted with the cavity. The probe is connect- The resonant wave length, or frequency, may be thus determined accurately. Since the foregoing formula does not apply to cavities of other shapes, such as a cylindrical cavity, the probe method of determining resonance is preferred. In any event the calculations are only a guide; the exact resonance is determined by any desired method of measurement.

Thus the invention has been described as a magnetron in which the anode includes longitudin'al'slits. Resonant cavity members, opening into the anode slits, are attached to the anode. The out-of-phase electrons moving past the slits give, up energy to establish and maintain within the resonant cavities standing electromagnetic waves. The waves may be applied to a coupling loop if the device is used as an oscillator 'or the currents in a load circuit may be'used' to establish electric waves within the cavity. These Waves are amplified or detected by the electrons spiralling within the anode electrode. The Waves in a plurality of cavities may be phasedby a coupling loop. The invention is not limited to any precise number of resonant cavities'of any specific shape. Furthermore, it should be understood that the resonant cavity may-be adjusted to respond to any desired frequency by employing means such as a Sylphonoperated tuning screw, plug, or pistoni 51 in each 'cavity'foradjusting the size or shape of the cavity, for example, as disclosed in U. S. Patent No. 2,233,263 which was granted on February 25, 1941, on an application Serial No. 243,- 211, filed November 30, 1938, by Ernest G. Linderj While the cavity members and anode have been described as included within an evacuated envelope, it should be understood that they may form their own envelope with the attendant advantages of cooling and the like.

I claim as my invention:

1. An ultra high frequency device including a cathode, a substantially cylindrical anode surrounding said cathode and including diametrically opposed symmetrically located longitudinal slits, a. plurality of cuneiform members each including a cavity resonator closed at its ends, said cavity resonator being effectively entirely closed to ultra high frequency standing waves which are to be established therein, each of said members including a longitudinal slit located at its apex and opening into said cavity'resonator, and each of said members secured to said anode with said each of said anode slits substantially coinciding with the apex slit of said members and said cuneiform members mounted about said anode, and

means adjacent said anode for creating a mag-" said cavity resonator being effectively entirely closed to standing waves which are to be estab -i lished therein, each of said members'including a longitudinal slit located atits apex and opening into said cavity resonator, and each of said mem bers secured to said anod with said each of said anode slits substantially coinciding with the apex slit of saidmembers and said cuneiform mem-' bers symmetrically mounted about said anode, and means adjacent said anode for creating a magnetic field having its lines of force substantially parallel to and surrounding the axis of said cylindrical anode.

3. A device as claimed in claim -1 including tuning means disposed externally of said cuneiform members and coupled thereto for adjusting the phaserelationship of the fields established in said cavity resonators.

' ERNEST G. LINDER.

. REFERENCES CITED The following references are of record in the file of this patent: UNITED STATES PATENTS Number Name a Date 2,123,728 Hollmann July 12, 1938- 2,106,770 Southworth et a1 Feb. 1, 1938 2,253,080 "Maslov' Aug. 19, 1941 2,295,680 Mouromtsefi et al Sept. 15, 1942' 2,348,986 Linder May 16,1944- 2,304,186 Litton Dec. 8, 1942' 2,283,895 Mouromtseffet a1 May 19, 1942 Hollmann Nov. 21, 19 37 

